According to Japanese Examined Patent Application Publication No. 8-32702, sulfur, and in particular, a thiophene, generally inactivates all hydrogenation catalysts to a significant degree.
In particular, according to a paper written by Mozingo [Journal of the American Chemical Society (J. Am. Chem. Soc.) Vol. 67, p. 2092 (1945)], a thiophene can be converted to a thiolane with a yield of 70%. However, this reaction requires 200% of a palladium catalyst to be added to the substrate. The use of this method on an industrial scale is economically disadvantageous.
Furthermore, it is known that a thiophene itself becomes a catalyst poison in catalytic hydrogenation of the thiophene [“Shokubai Kagaku Gairon” (Outline of Catalytic Chemistry) written by Tadao Shiba and two others, New edition, p. 121, 1956].
For the above reasons, in the reduction of a thiophene derivative by hydrogenation, a reaction example using a catalyst, which is a noble metal such as palladium without further treatment or a palladium catalyst carried on a support such as activated carbon, has rarely been described.
Japanese Unexamined Patent Application Publication No. 2000-327678 discloses the hydrogenation of a 2-alkenyl-3-aminothiophene derivative using a 5%-palladium carbon. The 2-alkenyl-3-aminothiophene derivative is represented by general formula (1):
(wherein R represents a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted aromatic hydrocarbon ring, a substituted or unsubstituted nonaromatic hydrocarbon ring, a substituted or unsubstituted aromatic heterocycle, or a substituted or unsubstituted nonaromatic heterocycle; R1, R2, R3, and R4 independently represent a hydrogen atom, or a linear or branched alkyl group of 1 to 12 carbon atoms; and R1 and R2, R3 and R4, R1 and R3, R1 and R4, R2 and R3, or R2 and R4 may be bonded together to form a cycloalkyl group). In the above hydrogenation, the content of the catalyst relative to the compound is about 10%. The recovery and the reuse of the catalyst are not described in the document. However, such a reaction, wherein no less than 10% of the catalyst is used in every reaction, cannot be performed economically on an industrial scale.